Clutch valves with vehicle forward-reverse sensing control pump



United States Patent [72] Inventor DanielB. Shore Niles,lllinois 211Appl.No. 855,436

May 12, 1969 Division of Ser. No. 689,549, filed Dec. 11, 1967, nowPatent No. 3,458,018

[22] Filed [45] Patented Nov. 17, I 970 [73] Assignee InternationalHarvester Company Chicago, Illinois a corporation of Delaware [54]CLUTCH VALVES WITH VEHICLE FORWARD- REVERSE SENSING CONTROL PUMP [50]Field of Search l92/4R, 3.5FP, 87.18, 87 I9, Inq(74), lnq( I03), lnq( I80),

Primary Examiner- Benjamin W. Wyche Attorney-Noel G. Artman ABSTRACT:Tractor having dump valve and forwardqeverse drive control employingsame, effective to automatically brake the tractor when reversing thetractor's direction of mo tion. The tractor has brakes, a reversibletransmission controlled by the dump valve, a range selector valve havinga control portion, and a run detector pump to sense direction of rollingmovement of the tractor and having a directionalized pump output. Thedump valve generally receives against pressure movable end areas thereofan output from the range selector valve and directs control pressure tooperate the brakes and transmission in alternation to one another and,specifically: receives against the pressure movable end areas thedirectionalized pump output so as to be hydraulically balanced in acentered position operating the tractor with transmission engaged andbrakes disengaged; receives against the pressure movable end areas anunbalancing force from the range selector valve control portion causingthe dump valve to shift off center and dump, neutralizing thetransmission and setting the brakes; and having valve springs effectiveto mechanically rebalance the dump valve attendant with slow down of therun detector pump, causing the dump valve to recenter, releasing thebrakes and engaging the transmission Inq(l37) [56] References CitedUNITED STATES PATENTS 3,348,644 10/1967 Hilpert I92/87.l9X I 3,437,1844/1969 Wilson l92/4R inanopposite drive setting.

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a $15 M P2 u R7! Patented Nov. 17, 1970 I or 3 Shnet INVENTOR DANIEL B.SHORE I ATTORNEY 2f Mm.

Patented Nov. 17, 1970 Shoat 01 a QM Wm INVENTOR w DANIEL B SHORE aATTORNEY Patented Nov. 17, 1970 3,5403

Sheet ,2 MS

I NVENTOR DANIEL n. SHORE WW ATTORNEY CLUTCH VALVES WlTH VEHICLEFORWARD-REVERSE SENSING CONTROL PUMP This invention relates to a vehicleprovided with conventional brakes, and to an interacting vehicletransmission pro-' vided therein-which is operated by a forward-and-reardrive control which is provided so that, when beingreversed, thetransmission at once neutralizes while the brakes are progressivelybeing applied automatically, and subsequently the'transmission goes intothe opposite or reverse drive setting as and when the brakes havebrought the still rolling vehicle to the point at or near standstill, atwhich point the brakes release automatically without delay.

In the foregoing manner, my invention provides for conditioning of theoperating mechanisms in the vehicle so that as each reverse shift isbeing completed, the takeover shock encountered by the reverse powerpath-through the transmission is materially reduced or substantiallyeliminated. While the invention is primarily applicable to loaders andindustrialcon struction and agricultural tractors, it has equalapplication to trucks and other vehicles equipped .with a transmissiondrive, particularly a power shift transmission.

By reverse as used in a less encompassing sense, is meant only thatcondition of the transmission for driving to the rear whereas reverse,as used in the encompassing sense of a reverse shift above, means achange either from rear drive to drive in the forward direction, or viceversa. Similarly, reversing the power path is an expression meaningchanging from rear drive to forward drive, or vice versa.

Shuttle work to-and-fro constitutes such a major part of the utility ofindustrial construction, agricultural, loader, and like vehicles. that asuitable power shift transmission or hydrostatic transmission isdesirable to expedite the speed changes and direction changes that are afrequent necessityto the operator. Problemsarise when shuttling manysuch vehicles because reverse shifting is tedious and time consuming,and very often puts the transmission under undue strain due to shockloading of the reverse power path in effecting the change of direction.

My invention alleviatesthe foregoing problems. it especially alleviatesthe situation arising firstin the forced reverse shift situationencountered with a power shift transmission and second arising in such ashort interval,.and without conditioning the-operating components of thevehicle, that the strain is excessive, as will now be explained.

Features, objects, and advantages will either be specifically pointedout or become apparent when, for a better understanding of theinvention, reference is made to the following description taken inconjunction with the accompanying drawings, which show a preferredembodiment thereof and in which:

FIGS. 1 and 2 are right side andrearend elevational views to small scaleand large scale, respectively, of a tractor embodying the presentinvention;

FIG. 3 is atop plan view of a detail of FIG. I; and

FIG. 4 is an hydraulic circuit, illustrated with single lines, of thetractor control system.

More particularly in FIG. 1 ofthe drawings, the rear portion of theillustrative vehicle which is shown is part ofa crawler tractor for usein moving, loading, or carrying earth or other material. Alongitudinally extending tractor frame 12 carries a body 14 of thevehicle and is carried by left and right longitudinal endless tracks 16and 18 disposed one on each lateral side of the frame 12. The vehicle 10proceeds in a straight line so long as the tracks 16 and 18 are drivenatthe same speed and the vehicle is steered when the speed of therespective tracks differs.

The interacting components providing the essential control parametersaccording to my invention comprise first, a range selector valve 20forming part of a transmission range selector control tower A andsecond, a run. detector comprising a transmission signal pump- 22 whichis connected to the sprocket drive pinion shaft 24 forming part-of asprocket final drive system B. The two components 20 and 22 interact ina varying manner to control a neutralizable transmission system F whichdrives the vehicle and an automatic power brake cylinder 26 which isconnected to a brake linkage 28 forming part of the vehiclebrakingsystem G.

By the term .neutralizabletransmission system E, what i mean broadly isany hydrostatic, hydromechanical, or mechanical drive, or a power-shift,friction drive such as includes at least one opposite brake or clutchwhich remains inactive to reverse the drive until a companion operativebrake or clutch has definitely been declutched, all having aneffectively de-coupled condition of receiving input and yet transmittingno power output.

BRAKES: MECHANlCAL CONNECTIONS-FIGURES I AND 2 Y The brake pedal linkage281s actuated by being either drawn forwardly by a brake pedal, notshown, or. pushed forwardly by the automatic power brake cylinder 26 toset the brakes of the vehicle braking system G. At the rear, the brakepedal linkage 28 is connected to a brake applying arm 30 which is pulledforwardly when the linkage is actuated. The arm 30 operates in amechanical path by means of an outwardly moving, push-rod connection 32and a longitudinal arm 34 of a pivot brake bellcrank 36 to apply acaliper brake against a brake disk 38 in the right sprocket final drivesystem B to the track 16. Similarly, the arm 30 operates by means ofanother outwardly moving, push-rod 40 to apply a caliper brake against abrake disk, not shown, connected in the left sprocket final drive systemto the track 18. The linkages on both sides are the same, and operatethe two caliper brakes simultaneously.

More specifically, the push-rod 32 and bellcrank arm 34 connectionpushes outwardly against the upper end 42 of a caliper lever which ispivoted at its lower end on a fixed pivot 44. A shoe, not shown, whichis carried by a pivot 46 on the caliper lever is forced against theadjacent brake disk 38 and the reaction is taken by the main case 48ofthe final drive.

BRAKES: HYDRAULIC CONNECTIONS-FIGURES 1.

AND 2 The brake pedal linkage 28 receives hydraulic assistance from two,transversely aligned pivot cylinders 50, the linkage 28 controlling thecylinders through valves 52 in communication with respective cylindersand carrying the respective valve operating levers or arms 54. Thelinkage 28 has a single connection to the two arms 54 jointly so as tooperate the cylinders 50 in unison. 1

As illustrated in H6. 2, each pivot cylinder bellcrank 36 has a lateralarm 56 in engagement with a pivot cylinder 50. The

arms pivot the b ellcranks 36 when two cylinders 50 extend, causingengagement of the vehicle braking system G at both sides of the vehicle.

STEERING DRIVE SYSTEM-FIGURES I AND 2 Each of the pivot cylinders 50 ispart of a series of three hydraulic boosters, each series being disposedat one side of the vehicle for controlling the sprocket drive pinionshaft 24 at that side to steer the vehicle. The valving for the boostersis included among the valves 52, and the arms 54 operate all suchvalves.

A steering drive system H includes right and left steering levers 56 and58 which are slightly forward of the operators seat 60 and which areoperated by hand so as to swing foreand-aft in vertical planes. Eachsteering lever has a separate connection, not shown, to an arm 54 foroperating the steering valving independently. The steering system H alsoincludes each ofthe brake disks 38 (FIG. 2).

Each of the sprocket drive pinion shafts 24 has one of the brake disks38 fast thereto, and also a pinion 62 fast thereto. The two pinionshafts 24 are jointly driven by a reversible pinion shaft 64 which thepower shift transmission system E drives, and one of the pinion shafts24 drives the run detector pump 22 by means of intervening gearing 66.

The pinion 62 on each shaft 24 meshes with a bull gear 68 in the finaldrive B at each side of the vehicle. Depending upon the gear reductiondesired, each bull gear 68 can directly drive the drive sprocket of theadjacent track or can be connected to the sprocket by reductionplanetary gearing, not shown.

RANGE SELECTOR VALVE-FIGURE 3 The body of the range selector valvecarries a range spool 70. mounted for rotationand reciprocation therein.A selector lever 72 has a pivot connection at its midportion to theforward end of the range spool 70 and causes the spool 70 to be set inappropriate positions as the lever 72 is moved by the operator among aneutral position indicated at N in solid lines, a forward neutralposition indicated at FN in broken lines, a reverse neutral positionindicated at RN in broken lines, and respective drive positions F1, F2,R1, and R2 which are opposite similar markings on a slotted gate plate74 mounted atop the transmission range selector control tower A. Theslot 76 in the plate 74 receives and guides the lever 72 and is ofageneral U shape.

The body of the range selector valve 20 has, in addition'to the drainlines indicated at D hereinafter, a set of oil lines con nected theretoincluding lines F2 and R2 as shown, and N, FN, RN, Fl, and Rl, notshown, the abbreviations being functional drive designations includingneutral (N).

CONTROL ClRCUlT-FIGURE 4 Regulator valving, not shown, provides main,lube or intermediate, and drain pressure at the respective pointsabbreviated by their functional designations M, L, and D, previouslyreferred to. For simplification, all points and lines designated D canbe maintained at the lube pressure L if desired.

The body of the range selector valve 20 is drawn so that it appears attwo points in FIG. 4, the range spool according to this manner ofillustration being split out and shown in both a longitudinal view 200and a transverse sectional view 20b for ease in understanding. The rangeselector valve 20 is connected via a set of transmission valves 78 withdirectional clutch packs in the transmission system E, specifically aforward speed pack 80 and a reverse speed pack 82. The alreadyenumerated set of oil lines interconnects the selector valve 20 and thetransmission valves 78, and four service lines 84, 86, 88, and 90interconnect inlet-outlet ports in the respective transmission valves 78and the clutch packs 80 and 82 to provide forward and reverse speedsettings in the transmission. Two shafts designated F1 and R1 extend toestablish the low speed forward and reverse drives in the transmissionsystem E, and two shafts designated F2 and R2 extend to establish highspeed forward and reverse drives, respectively. The clutch packs areconventional, neutralizing the existing drive setting without delay andprogressively engaging a drive as selected.

in brief, the range selector valve 20, which is a multiposition valve,and the run detector pump 22, which is a reversible pump, mutuallyoperate a comparator-dump valve spool CD among the transmission valves78to coordinate neutralization of the clutch packs 80 and 82 andtransmission, and application of the automatic power brake cylinder 26.In addition to having such coordinated action of neutralization andbrake application, the transmission system E and vehicle braking systemC also have independent operation for the usual purposes.

lNDEPENDENT TRANSMISSION NEUTRALlZATlONFlGURE 4 In the neutral settingof the range selector valve 20 wherein the range spool has the position20a as shown in its longitudinal view and the position 2017 as shown inits transverse sec tional view, all in solid lines, the four oil linesFl, F2, Rl, and R2 are connected in common to, and are at the pressureof, the drain line D.

The neutral line N on the valve 20 and the main pressure line M on thevalve are interconnected thereby, and a double check valve 92 leading tothe power brake cylinder 26 unseats in a rightward direction such thatthe oil line N communicates, and sustains main line pressure in, the rodend of the power brake cylinder 26. The force of the pressure in arod-end chamber 94, coupled with the force of a brake release spring 96in the chamber, overcomes the force of main line pressure M constantlymaintained in the head end chamber 98 of the cylinder 26. Any fluidtrapped in the head end is thereby forced through a check valve 100which unseats to allow the fluid to enter therethrough into the mainline M. The brake cylinder 26 is held in the foreshortened, brakerelease position.

Irrespective of whether the run detector pump 22 is stopped or beingoperated due to coasting of the vehicle in one direction or the other,there is no further pressure in an active circuit in the hydrauliccontrol and in such condition the transmission system F remains inneutral and the brake system G remains disengaged.

A similar condition obtains with the vehicle either stationary orcoasting, when the lever is moved into one of its additionaltransmission neutral positions RN or FN.

When the vehicle is coasting in either direction, e.g., forwardly, andthe range spool is rotated clockwise from the position shown in solidlines 20h so as to take a position to the right corresponding to thatsame forward direction of the vehicle, no further pressure occurs in anactive circuit in the hydraulic control. Coasting of the vehicle in thatdirection, e.g., forward, when the range spool is rotated leftwardlyfrom the position shown in the solid lines 20!) into thecounterclockwise position, causes fluid to flow indirectly from the Fside of the run detector pump 22, through a line .1, the valve 20b, aline R, and thence from one direction into a double check valve 102 inthe line R and against a pressure movable end area 104 carried by thecomparator-dump valve CD and physically located in a pressure operatingchamber I06 at that end. The run detector pump also directly appliespressure from a different direction into the double check valve 102 andagainst the same pressure movable area 104 carried by thecomparator-dump valve CD. An opposite pressure movable end area 124 onthe valve spoolCD is meantime connected by a double check valve 136 tothe drain side of valve 20 and to the suction side of the pump 22. Thespool CD perforce shifts to the right as viewed in FIG. 4, causing onlythe right side of the double check valve 92 to be relieved of pressurein a path from the valve 92, through an oil line 108, a gallery-shapedcommon transfer chamber in the set of transmission valves 78, a spoolundercut 112, and thence through a cored cavity 114 into a galleryshaped common lube pressure chamber I16.

50 while the transmission has not changed setting, the set of valves 78has been preconditioned for a change due to shift of the spool CD, andthe double check valve 92 has been preconditioned to change the brakecondition because only one side thereof(connected to oil line N) remainspressurized.

NEUTRALIZATION WITH AUTOMATlC BRAKING-FIGURE 4 This situation is made tooccurwhen the preconditioning just described exists, i.e., the vehicleis coasting in one direction, e.g., forward, when the range spool hasreached the transition position (RN) corresponding to the oppositevehicle direction. F mm the latter position, the spool from the positioncorresponding to the longitudinal view a is shifted rightwardly, as seenin that view, into the R1 position also known as low reverse. The onlypressurized oil line N connected to the double check valve 92 is ventedto drain D through the range selector valve 20, relieving pressure inthe rod end chamber 94 of the automatic power brake cylinder 26.

The brake system G is applied because the hydraulically unopposed mainpressure in the head end chamber 98 extends the cylinder 26 and, at thesame time, the oil line R1 applies main line pressure to a pressuremovable right end area 118 carried by the valve R2R1 and located in apressure operating chamber 120. The valve R2Rl moves leftwardly asviewed in FIG. 4, forming a drain path in which the fluid can flow fromthe right side of the clutch pack 82, through the line 90, and thencethrough an undercut 130 to transfer chamber 110 which is maintained atthe lube pressure level.

Hence, transmission system E remains in neutral during the decelerationperiod while the rolling vehicle is being braked by the braking systemG.

At some point during the terminal portion of deceleration of thevehicle, speed of the run detector pump 22 decreases until the pumpoutput pressure in the valve end chamber 106 is overcome by the force ofa spring 122 surrounding the pressure movable end area 124 presented bythe comparatordump valve spool CD in a pressure chamber receiving theright end of the spool CD. The spool CD mechanically recenters, betweenthe spring 122 and an opposite spring 138 balanced thereby, to itsneutral or satisfied position, blocking the cored cavity 114 which is atlube oil pressure and communicating main line pressure to the right endchamber of the reverse clutch pack 82 through a path leading from acored cavity 126 in the transmission valving 78 which is at main linepressure, through an undercut 128 in the spool CD, the transfer chamber110, and an undercut 130 in the leftwardly shifted transmission valvespool R2R1, thence through the service line 90 into the directionalclutch pack 82 to establish the R1 drive setting. The clutch packs areof well known commercial construction, providing a quick, low pressureslack take up prior to application of full clutch engaging pressure, tominimize shock ofengagement.

Simultaneously, the centered valve spool CD causes main line pressure tobe applied to the automatic power brake cylinder 26 in a path leadingfrom the cored cavity 126, through the undercut 128, the transferchamber 110, and the oil line 108, thence through the right side of thedouble check valve 92 and into the rod end chamber 94 of the cylinder 26to retract same and release the brake system G.

The vehicle then accelerates to the low speed in the desired oppositedirection, i.-e., R, and perforce the run detector pump 22 reversesdirection so that oil flows therefrom in the direction of arrow R in apath leading through a check valve 132, a valve and restriction type,maximum pressure regulating circuit 134, the oil line J, the range spool20b which occupies a leftward position from the position 20b shown inthe solid line sectional view, and the oil line R, thence through theupper half of the double check valve 102 and into the pressure chamber106.

Simultaneously, oil flows in the direction arrow R from the run detectorpump 22 through the bottom half of a double check valve 136 topressurize the pressure movable end area 124 on the valve spool CD.

As a result, the comparator-dump spool CD is hydraulically balanced andalso mechanically balanced by the previously described action of thesprings 122 and 138, each engaging one end of the spool opposite fromthe other. This hydraulic and mechanical balance of the spool CD in itssatisfied position continues as the reverse speed of the vehicleincreases, and will continue to be maintained if the selector valve isadvanced into the high speed reverse (R2) position for the purpose ofshifting the transmission into high speed reverse drive.

CONVENTIONAL DRIVE CHANGES-F1GURE 4 When proceeding rearwardly, thetransmission system E is readily shifted for the last-mentioned purposebetween R1 and R2 positions byreciprocatory movement of the rangeselector valve 20. The R1 condition has been described, and the R2condition is attended by main line pressure M being applied by theselector valve 20 through the oil line R2 into a pressure chamber-140. Apressure movable left end area 142 on the spool R2R1 is depressed underpressure, shifting the spool R2R1 to the right from the solid lineposition as viewed in FIG. 4. Main line pressure is thereupon directedby the valve R2R1 in a path leading from the cored cavity 126, throughthe undercut 128, the transfer chamber 110, and a longitudinal centralpassage 144 in the spool R2Rl which is cannelured, a set of radialpassages 146, valving 78, thence through the service line 88 into theleft chamber of the directional clutch pack 82 so as to cause high speedreverse drive in the transmission system E.

Changes in the forward drive range occur in conventional manner asresult of changing the range selector valve 20 between the F1 or F2positions, thereby applying main line pressure in a pressure chamber 148or 150 so as to shift the forward valve F1F2 respectively to the rightor to the left as viewed in FIG. 4. Main line pressure thus entersthrough the service line 84 into the left chamber or through the serviceline 86 into the right chamber of the directional clutch pack 80, theother service line and chamber being connected at the same time to thecommon lube pressure chamber I16 in the housing of the valves 78. v

In either of its directions of rotation, the run detector pump 22 alwaysdraws from one oil reservoir 152. One of a pair of seat-to-seatconnected checkvalves 154 unseats to connect the reservoir 152 to thesuction side of the pump 22, whereas the other one of the check valvesseats to block communication and stop escape of the pumped fluid fromthe output side of pump 22 back to the reservoir 152.

The check valve 132 unseats in the direction of a symmetricallydisposed, alternately operable check valve 156, which valves areconnected to the output side ofthe pump 22. When either valve isunseated to allow pump output fluid to flow into the regulator circuit134, the other valve stays seated to prevent loss of the regulatedpressure back to the suction side ofthe pump 22.

The regulator circuit 134 provides a continual restricted bleed to drainD from the oil line J and, in addition, prevents the pressure fromexceeding a predetermined value irrespective of the speed of the rundetector pump 22. At the lower pump speeds, the output falls below apredetermined reduced value, such that spring pressure of either spring138 or 122 readily overcomes the back pressure created by the circuit134 and recenters the spool CD.

A restriction 158 which is connected between main line pressure M andthe head end chamber 98 of the power brake cylinder 26 insures freedomfrom abruptness with a gradual application of the brake system G toprevent shock. The restriction 158 is contemplated by the check valve100 hydraulically in parallel therewith, so that the two form aflowcheck valve combination. On the other hand, the check valve 100unseats and bypasses the restriction 158 during the reverse flow causingbrake release, so that the brake system G can disengage immediately toexpediate vehicle direction changes.

The forward clutch pack has individual restrictions [60 symmetricallyconnected to the opposite actuating chambers therein so as to providefor a residual oil pressure forlubrication purposes in the chambers atall times. Similarly, the reverse clutch pack 82 has analogouslysymmetrically connected restrictions 162 for lubrication purposes, suchrestrictions all discharging to drain D.

The complete schematic circuit of the present hydraulic control, exceptfor certain novel additions hereof, appears in the same assigneescopending Ruhl U.S. Pat. application Ser. No. 507,010 filed Nov. 9,1965, the disclosure of which is incorporated in entirety herein byreference.

SUMMARY In summary, novelty is felt to reside in the beneficial resultscreated by the comparator dump valve CD. To illustrate the salientpoints, let us say that the vehicle 10 is rolling rearwardly. The valvespool CD has three phases of operation while thevehicleis so rolling. Inthe solid line position shown in FIG. 4, the valve CD in a first phasedirects high pressure fluid from the chambers I26 and 110 to the brakecylinder 26 to sustain the cylinder in the foreshortened, brake releaseposition; the valve CD also directs fluid from the chamber I I0 throughthe appropriate transmission valve and into the active end of theselected one 82 of the directional clutch packs to keep the transmissionengaged and sustain rolling of the vehicle rearwardly and under power.

In a second phase, the valve CD has an unbalanced position displaced tothe right or to the left from the solid line position shown in FIG. 4,actually to the left under the assumed rearward rolling condition. Suchposition of the valve CD is attendant with movement of the valve throughneutral to a selected forward driving position, whereupon the valve CDdumps the pressure of transfer chamber 110 through the low pressurechamber 114 doing two things. The brakes progressively engage due to thevalve CD dumping pressure from the rod end of the brake cylinder 26which takes its extended, brake-apply position; and the driving clutchpack 82 releases the rearwardly driving clutch therein because theclutch cylinder activating pressure is dumped through the service line88 or 90 leading to the transfer chamber 110 which is likewise beingdumped by the valve CD. The brakes force the coasting vehicle todecelerate.

In the third phase, the valve CD recenters into the balanced positionshown in solid lines in FIG. 4, restoring high pressure to the transferchamber 110. Consequently the brake cylinder 26 goes into theforeshortened brake release position as attained in the first phaseabove, but a selected clutch in the forward clutch pack 80 is activatedunder the high, engaging pressure to engage the transmission in forwarddrive and change the vehicle from the former rearwardly rollingdirection to the forwardly rolling direction desired.

The first phase of operation of the valve spool CD as just describedresults when the valve is hydraulically in balance from equal andopposite pressure forces on the pressure movable areas 104 and 124 atopposite ends of the valve CD. The run detector pump 22 appliesregulated output pressure to the end area 124 through a direct pathincluding the double check valve 136. The same regulated pump pressureis applied to the opposite area 104 through an indirect path leadingthrough the check valve 132, the lineJ connected to the valve 20, andthe valve 2011 which occupies a leftward tilted position from thevertical position as shown in FIG. 4 in solid lines, and thence throughthe line R, and the double check valve 102 to the pressure movable area104.

The second phase of operation of the valve CD when it is shiftedleftwardly from the position shown in solid lines in FIG. 4, occursbecause the prior pressure against area 104 is diverted when the valveoutput is transferred to the line F, in attendance with the fact thatthe pressure movable area 104 is thereupon relegated by the double checkvalve 102 to the low pressure or suction side of the pump 22 and to thelow pressure or drain side of the valve 20. t

For its third phase of operation in which the valve spool element CD isrecentered to its solid line position as shown in FIG. 4, the pressurearea 124 is relegated by the double check valve 136 to a predeterminedreduced pressure of the output side of the pump 22 and to apredetermined reduced pressure of the side of the valve 20 supplying theline F. In the third phase, the slow running run detector pump 22 cannotmaintain pressure above a predetermined reduced pressure because therestriction in the pressure regulating circuit 134 handles the outputunassisted and without build-up of appreciable back pressure across therestriction.

The converse result from the foregoing can readily be visualized,namely, the three similar phases which occur when the vehicle is rollingforwardly under power and the control is reversed to a rear driveposition. Circuit symmetry assures such result, the rolling vehicle ineither event being immediately declutched and progressively braked, andsub sequently being immediately unbraked and progressively clutched todrive in the opposite direction.

It is significant in my invention that the transmission maintainsdisengagement only a minimum period during reversal of movement, whichis valuable under the circumstances of rapid to-and-fro movement such asa crawler vehicle is utilized for. The spring tension in the recenteringsprings 138 and 122 is such that at a point prior to completion of thebraking down of the vehicle, the compressed one of those springs 138 or122 will overcome the diminishing pressure from the pump 22 and completethe power shift. Thus the selected driving clutch aids in reversing thevehicle direction by a somewhat premature engagement, either with orwithout assist from the brake cylinder 26 which, at some point, isdisengaged completely. This invention in the broad sense contemplates aslight overlap between the selected clutch and the brake cylinder 26 intheir operation, all prior to the point at which the vehicletransitorily reaches actual standstill.

It is appreciated from the preceding discussions under theneutralization headings that retention of the selector lever 72 in eachof the three neutral positions or movement of the lever into but notpast the neutral positions results in automatically holding the cylinder26 in the brake-release position. Yet conventional manual controlsremain available to set the brakes under those circumstances, as bypedal actuation or handle (H) actuation, with or without power assistsuch as from a brake booster cylinder (not shown) or the cylinders 50 or26.

lclaim:

1. In combination, a control valve assembly comprising:

a housing having high 126, transfer 110, and low 114, 116

pressure chambers;

a common bore intersection the chambers;

individual valve bores in communication with the transfer I10 and low116 pressure chambers and with plural service passages 84, 86, 88, insaid housing;

first and second range selector valve elements FIFZ, RZRI each shiftablydisposed in a different one ofthe individual valve bores, said valveelements being movable selectively from a position interconnecting thelow pressure chamber and the service passages to discrete operatingpositions at once interconnecting the transfer chamber and selectedservice passage and interconnecting the low pressure chamber and theunselected service passages;

a dump valve element CD shiftably disposed in said common bore andhaving an undlsplaced, satisfied position interconnecting the transferand high pressure chambers and a' displaced, dump positioninterconnecting the transfer and low pressure chambers;

means including pressure movable control means 104, I24 carried by thedump valve element for shifting same selectively to make available highpressure to, or to dump the pressure from, the transfer passage and theselected service passage;

utilization means for said control valve assembly comprising a vehiclesupported for rolling movement on a horizontal surface;

a run detector pump 22 connected to the vehicle to sense its directionof rolling movement and having a directionalized pump output; and

means including a desired direction selector 20 for controllingapplication of the pump output in two paths to said pressure movablemeans carried by the dump valve element each opposing and balancing theother so that said element takes an undisplaced, satisfied position whenpump is undesired; and

said dump valve element having means including a control device therefor138 or 122 effective to restore the dump valve element to theundispluced. satisfied position. when the pump output falls to or belowa predetermined reduced value indicative that rolling of the vehicle inthe undesired direction has reached a substantial standstill.

